Introduced, naturalised or invasive in East Africa

Habitat

Disturbed areas, roadsides, riverbanks.

Description

Ricinus communis is a long-lived (perennial) shrub with can grow to the size of a small tree in suitable conditions.

R. communis can vary greatly in its growth habit and appearance (Sabina et al. 2009). The variability has been increased by breeders who have selected a range of cultivars for leaf and flower colours, and for oil production. It is a fast-growing, suckeringperennialshrub which can reach the size of a small tree (around 12 metres tall), but it is not cold hardy.

The glossy leaves are 15-45 cm long, long-stalked, alternate and palmate with 5-12 deep lobes with coarsely toothed segments. In some varieties they start off dark reddish purple or bronze when young, gradually changing to a dark green, sometimes with a reddish tinge, as they mature. The leaves of some other varieties are green practically from the start, whereas in yet others a pigment masks the green colour of all the chlorophyll-bearing parts, leaves, stems and young fruit, so that they remain a dramatic purple-to-reddish-brown throughout the life of the plant. Plants with the dark leaves can be found growing next to those with green leaves, so there probably is only a single gene controlling the production of the pigment in some varieties at least. The stems (and the spherical, spinyseedcapsules) also vary in pigmentation. The fruit capsules of some varieties are more showy than the flowers.

The fruit is a spiny, greenish (to reddish purple) capsule containing large, oval, shiny, bean-like, highly poisonous seeds with variable brownish mottling. Castor seeds have a warty appendage called the caruncle, which is a type of elaiosome. The caruncle promotes the dispersal of the seed by ants (myrmecochory).

Reproduction and dispersal

Ricinus communis reproduces by seed with plants becoming mature in their first season. They are capable of flowering year round in a frost-free environment. The plant can seed prolifically. Seeds can be dispersed by rodents and birds, on mud adhering to boots, on vehicles and machinery and by floodwaters. It is also spread by an explosive mechanism (at local level) when the capsule dries up and splits. Taller plants can throw their seeds 5-plus metres from the mother tree.

Economic and other uses

Ricinin which can be extracted from the beans of castor oil is highly toxic and has been used in homicide. Castor oil has more benign uses as a soap and as vehicles or carriers, emollients or solubilisers for toiletries and cosmetics and are used for cleansing and conditioning the skin. The plant has medicinal properties. It is gaining popularity as a biodiesel crop.

Environmental and other impacts

Ricinus communis forms monospecific stands which can displace native plant species. It can invade neglected farmland and pasture. The seeds are poisonous if they are chewed and ingested. Seeds that are not chewed are likely to be harmless. The foliage is only slightly toxic.

R. communis has been listed as a noxious weed in the Australian states of New South Wales and the Northern Territories and as a Category 2 invader in South Africa (invaders with certain qualities, e.g. commercial use or for woodlots, animal fodder, soil stabilisation, etc. These plants are allowed in certain areas under controlled conditions).

Management

The precise management measures adopted for any plant invasion will depend upon factors such as the terrain, the cost and availability of labour, the severity of the infestation and the presence of other invasive species. Some components of an integrated management approach are introduced below.

The best form of invasive species management is prevention. If prevention is no longer possible, it is best to treat the weed infestations when they are small to prevent them from establishing (early detection and rapid response). Controlling the weed before it seeds will reduce future problems. Control is generally best applied to the least infested areas before dense infestations are tackled. Consistent follow-up work is required for sustainable management.

Ricinus communis can be controlled through cultivation and mowing or physical uprooting. Herbicides can be effective as cut stump treatments or basal bark applications (painting herbicide onto the bark).

When using any herbicide always read the label first and follow all instructions and safety requirements. If in doubt consult an expert. Fire can be used as a management tool, but usually in combination with other methods such as chaining. Fire alone may actually increase R. communis densities by plant regrowth and enhanced seed germination.

Legislation

Not listed as a noxious weed by the state or governments in Kenya, Tanzania and Uganda.

Notes

Castor seeds have been found in Egyptian tombs dating back to 4000 BC; the slow burning oil was used mostly to fuel lamps. Herodotus and other Greek travellers noted the use of castor seed oil for lighting, body ointments, and improving hair growth and texture. Cleopatra is reputed to have used it to brighten the whites of her eyes. The Ebers Papyrus is an ancient Egyptian medical treatise believed to date from 1552 BC. Translated in 1872, it describes castor oil as a laxative.

The use of castor bean oil ("eranda") in India has been documented since 2000 BC in lamps and in local medicine as a laxative, purgative, and cathartic in Unani, Ayurvedic and other ethnomedical systems. Traditional Ayurvedic medicine considers castor oil the king of medicinals for curing arthritic diseases (Kalaiselvi et al. 2003).

Castor seed and its oil have also been used in China for centuries, mainly prescribed in local medicine for internal use or use in dressings.

It was used in rituals of sacrifice to please the gods in early civilisations (Joshi et al. 2004)

Castor oil is known to have been used as an instrument of coercion by the paramilitary Blackshirts under the regime of Italian dictator Benito Mussolini. Dissidents and regime opponents were forced to ingest the oil in large amounts, triggering severe diarrhoea and dehydration, which could ultimately cause death. This punishment method was originally thought of by Gabriele D'Annunzio, the Italian poet and Fascist supporter, during the First World War.

Editors

Acknowledgments

This fact sheet is adapted from The Environmental Weeds of Australia by Sheldon Navie and Steve Adkins, Centre for Biological Information Technology, University of Queensland. We recognise the support from the National Museums of Kenya, Tropical Pesticides Research Institute (TPRI) - Tanzania and Makerere University, Uganda. This activity was undertaken as part of the BioNET-EAFRINET UVIMA Project (Taxonomy for Development in East Africa).